In view of the now well-established relationship between chlorofluorocarbons (CFC's) released into the atmosphere and the depletion of the earth's ozone layer, considerable attention is being directed to finding effective substitutes for these once widely used compounds. It appears that the worst offenders are the fully halogenated CFC's which contain chlorine. These compounds are relatively unreactive with other compounds in the lower atmosphere and thus are able to diffuse into the stratosphere intact and be decomposed by ultraviolet radiation to form, inter alia, chlorine compounds which readily react with ozone. On the premise that it is the chlorine constituent of the CFC's which ultimately reacts with and destroys the ozone molecules, and in the interest of approximating as closely as possible the physical properties of the CFC's already in use, the proposed substitutes have in general been HCFC's containing lesser proportions of chlorine or fluorocarbons containing no chlorine at all. For example, dichlorodifluoromethane, widely used under the trademark Freon 12 as a refrigerant in household refrigerators, in automotive units and in commercial freezers and display cases, has been replaced in many instances by 1,1,1,2-tetrafluoroethane (also known as R-134a) or by chlorodifluoromethane (also known as R22 or HCFC-22). Because R-134a is not miscible with many commonly used lubricants, mixtures of R-134a and R22 have been proposed for systems employing lubricants soluble in R22. See U.S. Pat. No. 5,198,139, Bierschenk et al, in this regard. In the recent past, over 90% of the chlorodifluoromethane and about a third of the dichlorodifluoromethane manufactured was utilized in air-conditioning and refrigeration.
With increasing recognition of the seriousness of atmospheric ozone depletion, stricter limitations on the future use of any chlorine-containing refrigerant continue to be imposed. One of the most suitable replacements for R22 in stationary refrigeration systems is a non-flammable mixture of the HFC compound difluoromethane, also known as R32, with other halocarbons or halohydrocarbons such as R134a and R125 (C.sub.2 HF.sub.5). One such mixture has been proposed which consists of 60% R32 and 40% R125. Another proposed mixture consists of 30% R32 , 10% R125 and 60% R134a. A significant problem in making this substitution arises from the fact that R32 is more reactive than R22 with the zeolite A commonly employed as an adsorbent-desiccant in the circulating refrigerant stream to protect against freeze-ups and corrosion of the refrigeration unit.